1. Field of the Invention
The present invention relates to a bipedal walking robot having a body and a pair of legs at both sides of the body.
2. Description of the Related Art
For a bipedal walking robot having a body and a pair of legs at both sides of the body, each leg thereof is composed of a thigh link connected to the body through a hip joint, a crus link connected to a lower end portion of the thigh link through a knee joint, and a foot connected to a lower end portion of the crus link through an ankle joint. There has been conventionally known a bipedal walking robot having a crus driving linear (translatory) actuator, which connects the thigh link and the crus link of each leg away from the knee joint, for driving the crus to rock around the knee joint, and a foot driving linear (translatory) actuator, which connects the crus link and the foot of each leg away from the ankle joint, for driving the foot to rock around the ankle joint with respect to the crus link according to a telescopic motion thereof, as disclosed, for example, in Japanese Patent Laid-open No. 2004-202676.
In this conventional bipedal walking robot, the foot driving linear (translatory) actuator is disposed backward to the crus link, in parallel to the crus link. Thereby, a telescopic force from the foot driving linear (translatory) actuator acts on a line parallel to a connection line connecting the knee joint and the ankle joint.
However, when the robot is walking on stairs, a flexion angle of the knee joint becomes greater and the crus link inclines forward greater with respect to the foot stepping on the surface of a step of the stairs. Therefore, in order to move upstairs, it is necessary for the foot driving linear (translatory) actuator to apply to the foot a greater moment in a direction declined forward around the ankle joint (declined direction of tip toes).
Herein, among the telescopic force of the foot driving linear (translatory) actuator, it is only a component in a direction orthogonal to the foot (ground surface) that contributes to the application of the moment to the foot. In the above-mentioned conventional example in which the telescopic force from the foot driving linear (translatory) actuator is applied to the line parallel to the connection line connecting the knee joint and the ankle joint, when the robot is walking on stairs, the connection line, i.e., the line of action by the telescopic force, inclines forward greater with respect to the foot. As a result, the component of the telescopic force from the foot driving linear (translatory) actuator is merely left acting on the direction orthogonal to the foot. Accordingly, it is impossible to efficiently apply the moment to the foot by the foot driving linear (translatory) actuator. In order to apply a desired moment needed to move upstairs, the foot driving linear (translatory) actuator has to be built into a large sized one with a high output.
In the conventional bipedal walking robot mentioned above, the linear (translatory) actuator for driving the crus and the linear (translatory) actuator for driving the foot are both composed of a driving unit having an electrical motor and a screw shaft driven to rotate by the electrical motor, and a slider provided with a nut member screwed to the screw shaft through a ball. The driving unit is provided with a guide frame longitudinal in a direction along a shaft line of the screw shaft (vertical direction), and the electrical motor is disposed at an upper end of the guide frame. The slider is engaged in a guide rail fixed in the guide frame in such a way that the slider can slide freely in the guide rail. The slider is configured to slide back and forth in the guide rail in the direction along the shaft line of the screw shaft by the rotation of the screw shaft.
The guide frame of the driving unit in the crus driving linear (translatory) actuator is rockably connected to the thigh link, and the slider of the crus driving linear (translatory) actuator is rockably connected to the crus link. The guide frame of the driving unit in the foot driving linear (translatory) actuator is rockably connected to the crus link, and the slider of the foot driving linear (translatory) actuator is rockably connected to the foot.
In order to improve motion performance (walking speed, responsibility) of the robot, it is necessary to decrease a moment of inertia of the thigh link and a moment of inertia of the crus link. However, in the above-mentioned conventional example, it is difficult to decrease the moment of inertia of the thigh link and the moment of inertia of the crus link. Specially, in the above-mentioned conventional example, each of the linear (translatory) actuators for driving the crus and the foot, respectively, is provided with the guide frame which is attached with the guide rail, longitudinal in the vertical direction and heavy, therefore, the center of gravity of each linear (translatory) actuator is considerably deviated downward from an upper end of the driving unit. Accordingly, although the driving unit is configured to be connected to the thigh link or the crus link so that the upper end thereof is at the same height as the joint (hip joint or knee joint) disposed at the upper end of each link, the distance between the center of gravity of each linear (translatory) actuator and the joint disposed at the upper end of each link will becomes greater. In addition, each linear (translatory) actuator becomes heavier due to the weight of the guide frame, which will make the moment of inertia around the hip joint of the thigh link and the moment of inertia around the knee joint of the crus link become considerably great.